7MM CAPS V 5MM CAPS

HI, Do Revolvers mostly use 7mm caps and Auto's 5mm , also can extra prop powder be added ( what ever that is?) I have been watching a lot of model gun videos and it seem's to be that the 7mm caps are louder also I have noticed that there are sparkle and non sparkle caps , is ther pros and cons with both kinds , thanks BILLY CAN

Both 7mm and 5mm caps should contain the same amount of red phosphorus.
Difference in loudness is mainly due to cartridge and replica design.
For example Marushin P38 is fairly quiet, while MGC 1911 is fairly loud - and they both use 7mm cap.
5mm cap is usually used when cartridge diameter is not large enough to contain 7mm cap (Marushin M17/XM177, Colt .25), or when designer preferred a smaller cap (Tanaka).
I think that Tanaka used mainly (only?) 5mm in their semi-automatics (P226, USP, Glock). Also Marushin in rifles (mentioned above), some revolvers (Kokusai Python?) and Hudson in their MadMax shotgun.

I think Smootik's right. Regarding the "sparkle". I believe both major branded caps, as well as the "real-flame" caps are made by Kane Cap Company. Seems to be my experience that the Marushin caps and RF caps have more sparks. The MGC branded caps have more smoke. I think it is all preference at that point - do you want sparks?

Yep I agree with Smootik as well. Regarding replica design, I recently tried changing the hammer spring tension on a derringer (which makes a very loud bang anway:)) and found that if more tension/ force were applied as the pin hits the cartridge / cap the louder the bang. So I guess loudness is also related to "speed" at which combustion occurs, ie all the powder at once across the whole face of the cap , and also the compression force, with a very weak spring I could reduce the bang to a phutt.

I would also think that in an "enclosed" piston cart, the length of the cart makes a difference, as when the cap is ignited the piston begins to move and Bang is released when piston clears the tight section of the bore, the length of the bore and the expansion of the gasses would (only in my opinion ) mean that in a short bore cart the gas / bang is released while under higher pressure than in a long bore cartridge?
So maybe for loudest bag, large det pin face, high force from striker, short cart lenght, tight as possible o-ring fit???

The "prop powder" you mention is quite possibly Magnesium shavings or fine powder which certainly can be used to create muzzle flash.
It's been the topic of discussion and experiment here for a long time.

Here are a few posts to ponder over:

https://mp40modelguns.forumotion.net/modelgun-videos-f2/muzzle-flash-sw-459-t1507.htm

https://mp40modelguns.forumotion.net/modelgun-videos-f2/mgc-abs-luger-p08-t1501.htm

https://mp40modelguns.forumotion.net/modelgun-videos-f2/claymore-s-pistols-muzzle-flash-t751.htm

https://mp40modelguns.forumotion.net/modelgun-videos-f2/claymore-s-wa-shan-pistols-muzzle-flash-t752.htm

https://mp40modelguns.forumotion.net/modelgun-general-discussion-f1/boom-or-pfft-t904.htm

https://mp40modelguns.forumotion.net/modelgun-general-discussion-f1/muzzle-flash-again-t748.htm

That should keep you going for awhile